How the Moken kids of Thailand can see underwater like dolphins

While the ability to see underwater was discovered among the Moken of Thailand, it turns out that with practice, most kids can achieve this superpower.
(Photo: JaySi/Shutterstock)

I used to dream I could breathe and see underwater, and every so often, I still partake of those nighttime reveries. But those sleeping fantasies were much more common when I was a kid, when my time was spent in lakes, rivers, pools and oceans. But research shows that seeing underwater isn't just the stuff of dreams. The children of the Moken people of Thailand, who spend their days in the water gathering shellfish, have an adaptation that allows them to do just that. And studies show almost any kid can learn to do the same.

The Moken, who live on the coasts (literally, in homes on stilts perched above the water) of Burma and Thailand, are semi-nomadic hunter-gatherers. While adults practice spear-fishing, the children contribute by free-diving for food — no goggles or flippers. And it seemed to a researcher who was in the area studying diving response, that the kids could see incredibly well underwater: "Erika Schagatay was in the south of China working with sea nomads...and noticed that the children were picking out small brown clams from among brown stones. To her, this was incomprehensible, as she could hardly see them with goggles, and the children used no such thing. It was not her area of science, so eventually it ended up on my desk," Anna Gislen, a researcher at Lund University in Sweden, told National Geographic.

So, given that her work focuses on visual processes in humans and animals, Gislen took off for the coast of Thailand to check it out. As she got to know the Moken, she watched the kids hunt, diving as deep as 75 feet. “They had their eyes wide open, fishing for clams, shells and sea cucumbers, with no problem at all,” she told BBC News.

The human eye is optimized to work in the air, not water, by refracting light through the outer cornea, which contains water. This is why it's important that our eyes are always wet — that thin layer of water helps us see. But when we open our eyes underwater, things get blurry. That's because that water is the same density as the fluids in our eye, so the light can't be refracted.

So how could the Moken kids see while swimming? Gislen guessed they somehow changed how their eyes worked, with some kind of alteration of the lens or pupil. After conducting some tests, she found that was exactly what was happening.

“Normally when you go underwater, everything is so blurry that the eye doesn’t even try to accommodate, it’s not a normal reflex,” says Gislen. “But the Moken children are able to do both — they can make their pupils smaller and change their lens shape. Seals and dolphins have a similar adaptation.”

But adults — whose lenses are stiffer — can't see underwater in this way.

And it's not just the Moken children who can do this. Gislen found both European kids who were on holiday in Thailand and Swedish kids from her hometown could develop this ability. She asked them to dive down and look at cards with lines printed in one direction or another to test them. It varied depending on the kid, but in the groups she looked at, all the kids were able to improve their vision underwater with practice (about 11 sessions). Apparently the Moken kids found these tests pretty fun.

A Moken village in Thailand's Mu Ko Surin National Park. (Photo: Gail Palethorpe/Shutterstock)

After the 2004 tsunami, the Moken were encouraged by the Thai government to move inland to permanent villages. The government employs the adults to work in the national park. When Gislen returned, their changed lifestyle meant kids weren't in the water as much as they had been previously. While the kids she had originally tested in 2004 still retained their amazing underwater vision as teenagers, she says they may be the last generation to have the ability.

But certainly not the last people.

When I was 13, I spent the summer in Nova Scotia on Cape Breton Island. I would sometimes hang out with two blonde-and-bronzed brothers, one a year older than me, the other a couple years younger. I'll never forget swimming in the choppy ocean waves off the coast with them — the younger brother repeatedly diving 30 to 40 feet down and grabbing lobsters and other sea creatures to show me as we bobbed at the surface, probably trying to impress me. I was mystified as to how he could pick the very well-camouflaged lobsters from the rocky seafloor. Now I know the answer — wherever there are kids who spend hours in the water diving for objects, their eyes will adapt to allow them to see the beautiful world beneath.